Reliability of operation is an important consideration for modern electronic devices, e.g., selective call receivers. One aspect of reliability is the device's ability to continue to function properly after exposure to an electrostatic discharge, e.g., a spark or the like. Conventional selective call receivers, e.g., pagers, generally include CMOS and bipolar circuits that are relatively sensitive to damage from high voltages such as those associated with an electrostatic discharge.
Various methods have been tried to protect the CMOS and bipolar circuits from damage due to phenomena such as junction breakdown, metal mask failure, or the like, caused by a high voltage electrostatic discharge. An example of two conventional protection schemes that form a low impedance path to ground for high voltages are spark gaps, e.g., closely situated pointed sections of a printed circuit board runner adjacent to a ground runner, or a zener diode. Neither of these alternatives completely protect the sensitive components since the energy associated with the electrostatic discharge has already entered the selective call receiver.
Accordingly, to alleviate the problems associated with electrostatic discharge, an apparatus must be fabricated that effectively isolates the sensitive circuitry within the selective call receiver from the energy contained within the electrostatic discharge, thus eliminating the possibility of damaging the circuitry and insuring continued reliable operation of the selective call receiver.